linux-kernel - Re: Queue upcall locking (was: [dm-devel] [RFC][PATCH] fix dm_any_congested() to properly sync up with suspend code path)

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Date:	Tue, 11 Nov 2008 13:22:11 -0500
From:	Christoph Hellwig <hch@...radead.org>
To:	Mikulas Patocka <mpatocka@...hat.com>
Cc:	Alasdair G Kergon <agk@...hat.com>,
	Christoph Hellwig <hch@...radead.org>, axboe@...nel.dk,
	dm-devel <dm-devel@...hat.com>, linux-kernel@...r.kernel.org
Subject: Re: Queue upcall locking (was: [dm-devel] [RFC][PATCH] fix
	dm_any_congested() to properly sync up with suspend code path)

On Mon, Nov 10, 2008 at 09:40:18AM -0500, Mikulas Patocka wrote:
> > - If the device is suspended, the response should be that it is 
> > congested, I'd have thought.
> 
> Yes, but these congestion upcalls are used only for optimization and the 
> device is suspended for so small time, that it doesn't matter if we 
> optimize io acces in small moment or not.

We use device congested to not block pdflush on a device that can't
currently accept I/O.  For a suspended device congested is always
correct, pdflush will just come back a little later and in the mean time
write out stuff that doesn't delay it.

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